[az containerapp compose create] Support to enable Managed Identities for accessing to Azure App Configuration

### Describe the bug

Pls kindly consider to add a support for enabling a Managed Identity (System-Assigned or User-Assigned Identity) to access an Azure App Configuration store from Container Apps.

### Related command

az containerapp compose create

### Errors

N/A

### Issue script & Debug output

N/A

### Expected behavior

It would be great if that command supports to create a Managed Identity for accessing to an App Configuration store and loading the environment vars (app configuration = app settings + connection strings).

### Environment Summary

```
azure-cli 2.60.0 *

core 2.60.0 *
telemetry 1.1.0

Extensions:
aks-preview 3.0.0b13
azure-devops 1.0.0
containerapp 0.3.50

Dependencies:
msal 1.28.0
azure-mgmt-resource 23.1.0b2
```

### Additional context

Every time a Container App has been deployed from Azure DevOps with that command, the environment vars are completely lost.